Novel Arabidopsis jasmonate-responsive mutants have variations in bacterial disease resistance

Jasmonates (JAs) regulate a wide range of developmental processes in plants and play a central role in regulating plant defense against biotic stresses such as pathogen infections and insect attacks. A transgenic Arabidopsis line containing the JA inducible VSP1 promoter linked to the Luciferase (LUC) reporter gene was mutagenized using random T-DNA insertion tags. Previous genetic screening of these lines through LUC activity identified 12 Arabidopsis mutants with reduced (jas mutants) or enhanced (jae mutants) PVSP1::Luciferase reporter gene expression upon JA treatment. Here we report phenotypic evaluation of these mutants in response to pathogen infection using Pseudomonas syringae pv. tomato DC 3000 strain. Out of 12 JA-related mutants, five (jas1, jas2, jas5, jas9 and jae1) showed increased susceptibility compared to the parental line, while one mutant (jas7) expressed significant resistance to the bacterial DC 3000 strain. Further molecular characterization of the selected resistant (jas7) and susceptible (jas1) mutants was conducted. Although both mutants were identified as jasmonate-signaling suppressors (jas) at the protein level, the LUC gene was constitutively expressed in jas7 at the mRNA level, while it was abolished in jas1. On the other hand, the endogenous VSP1 gene was constitutively expressed in jas1, but not in jas7 and the parental line. In addition, the expression of two pathogen responsive marker genes (PDF1.2 and THI2.1) were constitutively expressed in the disease resistant mutant (jas7), while expression in the disease susceptible mutant (jas1) was nearly undetectable before JA treatment. Genetic analysis of the jas1 mutant in an F2 segregation population demonstrated that a single recessive gene in jas1 regulates its disease susceptibility.